RT Journal Article
SR Electronic
T1 mGluR5 Antagonist-Induced Psychoactive Properties: MTEP Drug Discrimination, a Pharmacologically Selective Non–NMDA Effect with Apparent Lack of Reinforcing Properties
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 155
OP 164
DO 10.1124/jpet.113.211185
VO 349
IS 1
A1 Swedberg, Michael D. B.
A1 Ellgren, Maria
A1 Raboisson, Patrick
YR 2014
UL http://jpet.aspetjournals.org/content/349/1/155.abstract
AB Fenobam [N-(3-chlorophenyl)-N′-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl)urea], a potent metabotropic glutamate mGluR5 receptor antagonist, reported to have analgesic effects in animals and anxiolytic effects in humans, also caused adverse events, including psychostimulant-type effects and “derealization phenomena.” Recent electrophysiologic, pharmacologic, and anatomic data show that the mGluR5 antagonists 2-methyl-6-(phenylethynyl)pyridine (MPEP) and (E)-2-methyl-6-styryl-pyridine (SIB-1893) can inhibit NMDA receptor–mediated activity and that mGluR5 receptors are highly expressed in limbic and forebrain regions. The present studies first evaluated the potential of mGluR5 receptor antagonists to cause PCP-like psychoactive effects in a rat drug discrimination procedure and, second, explored and characterized the selective mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) as a discriminative stimulus and compared MTEP with other drugs known to be psychoactive in humans. Additionally, the reinforcing potential of MPEP and MTEP was compared with phencyclidine (PCP) in a rat intravenous self-administration procedure. Dizocilpine [(+)-MK-801] and ketamine caused full PCP-appropriate responding. Memantine and the mGluR5 antagonists caused no or weak partial PCP-appropriate responding. In MTEP-trained rats, MTEP, MPEP, and fenobam caused full and equipotent MTEP-appropriate responding. (+)-MK-801 and memantine caused MTEP-appropriate responding below 70%, whereas PCP, chlordiazepoxide and LSD caused MTEP-appropriate responding below 50%. Δ9-Tetrahydrocannabinol, yohimbine, arecoline, and pentylenetetrazole all caused MTEP-appropriate responding below 20%. Rats self-administered PCP but not MPEP or MTEP, indicating a lack of reinforcing effects of the mGluR5 antagonists. These data suggest that the mGluR5 antagonists appear not to have reinforcing properties, that the discriminative effects of mGluR5 antagonists and PCP are dissimilar, and that mGluR5 antagonists may produce psychoactive effects different from NMDA-antagonists and other drugs with known psychotomimetic properties.